New York Times - 2 Jun 98

Lush Life: What Will We Lose as More Species Vanish?

By WILLIAM K. STEVENS
June 2, 1998

To Many, Out of Sight...

Biologists and the public see the world
differently in regard to environmental threats, recent
polls show.

Biologists overwhelmingly view the loss
of biodiversity -- that is, the loss of different species
of plants and animals and their habitats -- as the most
serious environmental problem, but the public is mostly
unfamiliar with the concept of biodiversity and considers
pollution the biggest threat.

Most biologists say the world is
experiencing a mass extinction of plant and animal life,
mainly a result of human activity, according to the poll,
which was conducted for the American Museum of Natural
History by Louis Harris & Associates. The nationwide
survey of 400 biologists taken from the membership of the
American Institute of Biological Sciences was conducted
in January and February.

The majority of biologists agree that if
trends continue, the loss of plant and animal species
will have a very negative effect on the earth's ability
to recover from both natural and man-made disasters.
"When a species is driven to extinction, that's it," said
Dr. Stuart Pimm, a professor at the University of
Tennessee who specializes in endangered species. "The
potential of that species for our benefit is lost."

The museum also commissioned a Harris
poll of the public, asking some of the same questions of
1,000 adults nationwide in January. Most say they do not
believe a mass extinction is occurring. Mass extinction
is defined by some scientists as a rate of extinction 100
to 1,000 times the natural rate.

Pollution is seen as the single most
important environmental threat by 62 percent of the
adults surveyed.

Biologists consider the earth more
threatened by population growth (39 percent) and loss of
biodiversity (22 percent).

"Pollution is obvious -- you can see it
and smell it," Dr. Pimm said. "But pollution can be
reversed, while extinction is irreversible."

MARJORIE CONNELLY

It is difficult to know for sure, but there may be
more kinds of creatures living on earth now than ever before in the
planet's 4.6-billion-year history. Or at least there were that many
before human beings appeared very late in the game and began changing
the rules.

At first, life consisted of microscopic, single-cell
balls, rods and filaments.

For perhaps three billion years, these blue, green,
purple and white microbes were all the life there was, all the
decoration available to a wet, stark and rocky world.

Not until about 600 million years ago, after the
earth emerged from its deepest ice age ever, did bigger species evolve.
Then life's variety exploded.

The expansion of biological variety has been on an
upward curve since then.

From sequoias and nematodes to fungi and elephants,
from poison ivy and jellyfish to eagles, cockroaches, spiders and algae,
millions of species -- the vast majority undiscovered and unnamed by
humans and most of them very small -- populate the world.

The curve has not been a smooth one.

At least five times in the last 600 million years,
planetwide environmental cataclysms, like drastic climatic change and
colliding asteroids, have wiped out whole families of organisms. Such
events have threatened to erase life, but succeeded only in partly
clearing the stage for new and different families.

Between extinction spasms, in the background hum of
evolution, single species winked out here and there to be replaced by
new ones.

Because of this continuous turnover, scientists
believe, more than 95 percent of all species that have ever existed are
extinct today.

Now one species, Homo sapiens, has become so
dominant on the planet and so powerful an influence on the rest of the
biosphere that many experts fear it is perpetrating, willy-nilly, a
sixth major extinction.

If so, it is happening simply because people are
acting naturally -- harvesting wild species to burn, eat or sell;
expropriating and destroying wild habitat to make way for human works
like farms, cities and suburbs; moving plants and animals around the
globe in a mix-and-match game in which a relatively few, superadaptable
plant and animal species are crowding out a larger number of less hardy
ones.

The pressure is likely to intensify as the earth's
human population, now about six billion, approaches a doubling before
leveling off in perhaps a century.

The impact of the numbers, now and in the future, is
magnified greatly by technology's power to shape the landscape and
exploit the oceans.

This combination has been especially worrisome for
the rain forests, where most of the world's species are found and
large-scale clearing is under way.

No one knows exactly how many species live on
earth.

About 1.4 million have been described and named, but
biologists believe there are at least 10 times that many.

And no one can put precise numbers on the rate of
present-day extinction, although several scientists have made rough
stabs.

One relatively conservative estimate says that for
some species found only in one locality, the rate may be 100 to 1,000
times the normal "background" rate between mass extinctions of the
past.

Despite the difficulty of making exact or even
reasonably approximate measurements, few scientists who study the
situation doubt that humans, by proceeding with business as usual, are
driving other creatures toward extinction at a growing rate.

To whatever extent they are doing so, people are
reducing the variety of life on earth -- what conservation biologists
now call biological diversity, or just biodiversity.

Biodiversity is not merely a matter of different
kinds of species.

It applies to many layers of nature on different
scales.

On one level, it is expressed by the number of
genetic variations within a species, the raw material of evolution;
destroy the wrong genes, and the species might not be able to adapt and
survive in the long run.

On a broader scale, biodiversity is expressed in the
bewildering variety of types of ecosystems, the tightly interwoven
communities of plants, animals and microbes that are nature's working
units.

Forests, wetlands and grasslands are examples of one
level of ecosystem variety, and each comprises numerous interconnected
subunits, right down to the microscopic.

It is these interconnected communities that
constitute the fabric of life on earth.

To whatever degree human activity is narrowing the
variety of life, scientists say, it is doing so on all levels.

Why does this matter? Conservationists and
biologists offer a number of answers.

On the practical level, wild species provide the raw
material for medicine and food. Who knows what undiscovered plant might
provide a cure for our era's killer diseases? Acting together, wild
species support the human economy by providing an array of services like
water purification, soil formation, pollination, flood control and, in
our age, outdoor recreation.

On a more fundamental level, they support human life:
without humans, the biosphere would not miss a beat.

But without insects and microbes, humans would
disappear quickly.

Some experts say natural systems are intrinsic to
psychological well-being. Finally, many conservationists assert a moral
imperative: it is simply wrong to destroy large slices of creation.

Moral arguments aside, are all species equally
valuable? Scientists believe that in many ecosystems, a few keystone
species hold everything together, and that if they are removed, the
system will collapse and all the other species in it will disappear.

The problem is that in most instances, no one is sure
which are the crucial species.

What's more, scientists have found, the greater the
variety of plant species in an ecosystem, the more productive it is over
all.

So, conservationists argue, it is necessary to save
as many species as possible.

They have their work cut out for them, since the
catalogue of imperilment is long.

In April, the World Conservation Union, in Gland,
Switzerland, added nearly 34,000 plant species -- 1 of every 8 known
plant species in the world, and nearly 1 of 3 in the United States -- to
its growing "red list" of imperiled organisms. Previously, the group
placed nearly a quarter of all mammals and more than 10 percent of bird
species on the list.

In possibly an even more important gauge of overall
biological vitality, an earlier assessment, by United States Federal
Government scientists, found that vast stretches of the natural
landscape, amounting to at least half the area of the contiguous 48
states, had declined to the point of endangerment.

This report, the first ever done on the state of
health of the nation's individual ecosystems, found that 30 of them,
some of which dominated vast regions before the arrival of Europeans,
have been destroyed or degraded by 98 percent.

If they were to disappear, entire assemblages of
species would vanish.

The individual species most at risk are those
existing only in one small area, like on an island or in a particular
river in the United States or, in some cases, even on a single tropical
mountainside.

These endemic species, as they are called, account
for most of whatever extinctions are in progress now, scientists
believe.

Not even the trackless ocean is immune. Overfishing
has pushed some marine species -- the cod and the blue-fin tuna, for
example -- to the brink of commercial extinction.

Coral reefs in some parts of the world are under
severe assault; in parts of Asia, fishermen squirt sodium cyanide into
the water to stun fish, in doses strong enough to kill the corals that
maintain the reef ecosystem.

The abundant evidence for the threat to biodiversity
should not be overinterpreted. It does not necessarily mean that many of
the species thought to be imperiled will disappear immediately, or even
within many years.

The recent red-listing of plants includes many simply
because they are rare.

While many may be vulnerable, humans do not threaten
them just yet.

The red list of plants can be read another way, too:
while 1 in 8 plants was judged imperiled, almost 90 percent were
not.

Some conservation biologists, fearing that the sixth
extinction is in its early stages, see no cause for comfort here. But
others say there is still time for action.

On the action front, there are bright spots. Over
the last century, a worldwide conservation movement has struggled to
stem the human assault on nature.

The United States' Endangered Species Act is regarded
as the strongest protection law in the world.

In the last six years, more than 160 countries, not
including the United States, have ratified a treaty obligating
governments to to protect plant and animal species.

A growing restoration movement has begun to reverse
the trend toward biotic impoverishment in some places.

Restoration projects have achieved eye-catching
results: in the resurgence of Midwestern prairies and oak savannas; in
Yellowstone National Park, where wolves are thriving again, and on the
southern Plains, where buffalo roam once more.

But victories are scattered, hard won and subject to
reversal or cancellation.

Recently, a Federal court, for instance, invalidated
the Yellowstone wolf restoration project, and a legal battle is under
way.

Meanwhile, habitat continues to disappear at an
"unprecedented" rate, according to the United Nations.

The magnitude of the sixth extinction, if that is
what is occurring, will become clear in time.

If the extinction turns out to be in the class of the
five big ones of the past, that should be made abundantly evident in the
decades ahead.

If so, the world can expect to recover its lost
biological diversity slowly, in 5 million to 10 million years --
assuming the extinction spasm can be controlled.

The 21st century may reveal whether the clever brain
bequeathed to Homo sapiens by the evolution of biological diversity can
be used to save diversity as well as destroy it.

William K. Stevens covers environmental sciences
for The New York Times.